(1) Field of the Invention
The present invention relates to the method for filling containers, in particular capsules comprising a bottom portion and a lid portion, with metered quantities of powdered materials, in particular, pharmaceutical materials.
(2) Prior Art
In general, capsules are filled with powder drawn from a supply trough by means of respective dosing devices, each comprising a tubular vertical punch. Inside the tubular vertical punch is an ejection piston slidably mounted for reciprocating movement. Each ejection piston is moved, in use, relative to the respective punch between a lower position, in which a lower end of the piston is flush with the lower open end of the punch, and an upper position, in which the lower end of the piston is arranged above the lower end of the punch so as to define, inside the tubular punch, a dosing chamber. In other words, the lower end of the punch, which is normally open, is closed by the piston during operation. Moreover, in use, each dosing device is moved axially between an upper position, in which the lower end of the punch is arranged above the upper surface of the powder in the supply trough and a lower position, in which the lower end of the punch is arranged in contact with the bottom of the supply trough.
In the known filling devices for capsules, each dosing device is normally advanced transversally of its vertical axis, which is generally a circular path extending along the periphery of a conveying drum. The conveying drum is mounted for rotation about a vertical axis and is provided with a plurality of equally spaced vertical through bores, each of which is slidably engaged by a punch of a respective dosing device. The above rotary drum is arranged above a rotary container, which defines the aforementioned supply trough, and is rotated, in use, at substantially the same speed as the above conveying drum.
In this known filling devices for capsules, each dosing device operates as follows: at the beginning, each dosing device is advanced by the conveying drum with the punch arranged in its upper position and above the upper surface of the powder in the rotary container, and with its piston arranged in its upper position relative to the punch so as to define therein the aforementioned dosing chamber. Upon reaching a predetermined position, each dosing device, while being advanced by the conveying drum, is moved downward to its lower position, with its piston remaining in the upper position relative to the punch. This downward movement results in the dosing chamber being substantially filled up with powder. The piston is then moved slightly downward relative to the punch toward its lower position, with the punch remaining in its lower position in contact with the bottom of the rotary container, so as to compact the powder within the dosing chamber. The dosing device is then moved upward to its upper position together with the compacted powder dose inside its dosing chamber. The piston is finally moved downward relative to the punch to its lower position to reduce the volume of the dosing chamber to zero and eject the compacted powder dose at a loading position. The loading position is where the bottom portion of the capsules to-be-filled are advanced. In this way, the bottom portion of each capsule is filled in succession with respective powder doses at the loading position. The bottom portion of each capsule is then advanced to a closing position where each bottom portion is closed by a respective lid portion.
The known filling sequence described above suffers from a major drawback in that some air remains normally trapped inside the dosing chamber when, at the beginning of the sequence, the dosing device is lowered into the powder to its lower position with the piston arranged in its upper position inside the punch. Owing to a portion of the dosing chamber being occupied by air, the final compacted powder dose may not correspond to the predetermined dose to be obtained.
According to U.S. Pat. No. 3,847,191, the above problem is solved by making either each piston or the bottom of the rotary container of porous material, and by applying a suction through the porous material when the powder is being compacted inside the dosing chamber so as to extract the trapped air therefrom.
The above solution, though very ingenious, is not very often employed due to the cost involved; to the relatively low mechanical resistance of the porous material used; and above all, to the fact that very fine powders tend to pass through the porous material and pullute the ambient environment.